1. Field of the Invention
The present invention relates to a supporting apparatus and method, a stage apparatus using the same, and an exposure apparatus. The invention is suitable for self-weight compensation for a fine-movement stage, such as a wafer positioning stage apparatus of a semiconductor exposure apparatus, and more particularly, for self-weight compensation for a fine-movement stage in which six axes are subjected to direct positioning control by a linear motor.
2. Description of the Related Art
FIGS. 7A and 7B illustrate the detail of a wafer stage apparatus mounting a fine-movement stage in which six axes (six degrees of freedom) are subjected to direct positioning control by a linear motor, in a semiconductor exposure apparatus: FIG. 7A illustrates a state in which the apparatus is partially exploded; and FIG. 7B is a perspective view illustrating an assembled state of the apparatus.
In this wafer stage apparatus, a Y guide 2 is fixed on a base plate 1. A Y stage 3, guided by a side of the Y guide 2 and the upper surface of the base plate 1, is supported by an air slide (not shown) so as to be slidable in the y-axis direction on the base plate 1. The Y stage 3 principally includes four members, i.e., two X guides 4, a front-end member 5, and a rear-end member 6. The rear-end member 6 faces the side of the Y guide 2 and the upper surface of the base plate 1 via air pads (not shown) provided at a side and the lower surface of the rear-end member 6. The front-end member 5 faces the upper surface of the base plate 1 via an air pad (not shown) provided at the lower surface of the front-end member 5. As a result, as described above, the entirety of the Y stage 3 is supported so as to be slidable in the y-axis direction by the side of the Y guide 2 and the upper surface of the base plate 1.
On the other hand, an X stage 7, serving as a component of the Y stage 3, guided by the lower surfaces of the two X guides 4 and the upper surface of the base plate 1 is provided so as to surround the Y stage 3 around the x axis, and is supported so as to slidable in the x-axis direction by an air slide (not shown). The X stage 7 principally includes four members, i.e., two X-stage side plates 8, an upper plate 9, and a lower plate 10. The lower plate 10 faces the upper surface of the base plate 1 via an air pad (not shown) provided at the lower surface of the lower plate 10. The two X-stage side plates 8 face sides of the two X guides 4, serving as components of the Y stage 3, via air pads provided at sides of the X-stage side plates 8. The lower surface of the upper plate 9 and the upper surface of the X guide 4, and the upper surface of the lower plate 10 and the lower surface of the X guide 4 do not contact each other. As a result, as described above, the entire X stage 7 is supported so as to be slidable in the x-axis direction by the sides of the two X guides 4 and the upper surface of the base plate 1. In FIGS. 7A and 7B, there are also shown a front-side mounting plate 13, and a rear-side mounting plate 14.
One and two polyphase coil-switching-type linear motors X1, Y1, Y2 are used for x-axis-direction driving and y-axis-direction driving, respectively, as a driving mechanism. FIGS. 10A-10D are diagrams illustrating this driving mechanism: FIG. 10A is a plan view; FIG. 10B is a longitudinal cross-sectional view; FIG. 10C is a side view; and FIG. 10D is a plan view of a portion around a lower yoke. A stator is obtained by inserting a plurality of coils 16 arranged on a coil holder 15 that is long in the direction of the stroke, into a frame. A movable member comprises a box-shaped magnet unit in which movable magnets 18a and 18b are disposed at the inner surfaces of an upper yoke 17a and a lower yoke 17b connected by two side plates 19, respectively. This linear motor generates a thrust by selectively supplying a current to the coil 16 of the stator depending upon the position of the movable member.
FIG. 8 is an exploded perspective view illustrating the detail of the fine-movement stage. The fine-movement stage is provided on the upper plate 9 of the X stage 7, and positions a wafer, serving as an object to be positioned, in a z-tilt direction and a θ direction. Positioning is performed by moving a top plate 11 in the xy θ direction and in the z-tilt direction by driving three z-axis-direction fine-movement linear motors ZLM (each including a movable member ZLMa and a stator ZLMb), two x-axis-direction fine-movement linear motors XLM (each including a movable member XLMa and a stator XLMb), and two y-axis-direction fine-movement linear motors YLM (each including a movable member YLMa and a stator YLMb).
FIGS. 11A-11F illustrate the fine-movement linear motors. As shown in FIGS. 11A and 11B, the z-axis-direction fine-movement linear motor ZLM includes the movable member ZLMa and the stator ZLMb. The stator ZLMb includes a flat coil 21Z whose longer side is parallel to the horizontal line, and a coil holder 22Z for holding the flat coil 21Z. The coil holder 22Z is fixed to an intermediate plate 12, which is shown in FIG. 8.
The movable member ZLMa includes four magnets 23Z facing at a longer side of the flat coil 21Z via a gap, two yokes 24Z for circulating the magnetic fluxes of the magnets 23Z, and two side plates 25Z for connecting the two yokes 24Z. The movable member ZLMa is fixed to the top plate 11. In the z-axis-direction fine-movement linear motor ZLM, when a current is supplied to the flat coil 21Z, a force in the z-axis direction is applied between the flat coil 21Z and the magnetic yoke assembly.
As shown in FIGS. 11C and 11D, the y-axis-direction fine-movement linear motor YLM includes the movable member YLMa and the stator YLMb. The stator YLMb includes a flat coil 21Y whose longer side is parallel to the vertical line, and a coil holder 22Z for holding the flat coil 21Y. The coil holder 22Y is fixed to the intermediate plate 12.
The movable member YLMa includes four magnets 23Y facing at a longer side of the flat coil 21Y via a gap, two yokes 24Y for circulating the magnetic flux of the magnets 23Y, and two side plates 25Y for connecting the two yokes 24Y. The movable member YLMa is fixed to the top plate 11. In the y-axis-direction fine-movement linear motor YLM, the movable member YLMa and the stator YLMb are arranged so that the normal of the flat surface of the flat coil 21Y is directed in the x-axis direction, in order that, when a current is supplied to the flat coil 21Y, a force in the y-axis direction is applied between the flat coil 21Y and the magnetic yoke assembly.
As shown in FIGS. 11E and 11F, the x-axis-direction fine-movement linear motor XLM is entirely the same as the y-axis-direction fine-movement linear motor YLM, except that the mounting direction differs. The movable member XLMa and the stator XLMb are arranged so that the normal of the flat surface of the flat coil 21X is directed in the y-axis direction, in order that, when a current is supplied to the flat coil 21X, a force in the x-axis direction is applied between the flat coil 21X and the magnetic yoke assembly.
A square mirror (not shown) is formed at a side of the top plate 11, so that the positions of the top plate 11 in six-axes directions can be precisely measured by a laser interferometer.
In the above-described configuration, a wafer is first mounted on the top plate 11 by a conveying system (not shown). Then, the top plate 11 is precisely positioned in x, y, z, θ and tilt directions by performing appropriate current control for respective coils of an x-axis-direction coarse-movement linear motor X1, two y-axis-direction coarse-movement linear motors Y1 and Y2, the three z-axis-direction fine-movement linear motors ZLM, and a fine-movement motor θ, by a control system (not shown). Then, a pattern on an original (not shown) is successively exposed and transferred on the wafer by performing exposure using exposure means (not shown).
FIGS. 9A-9D illustrate a wafer mounting operation. FIGS. 9A and 9B illustrate the position of the fine-movement stage during exposure: FIG. 9A is a diagram as seen from the x-axis direction; and FIG. 9B is a diagram as seen from the y-axis direction. FIGS. 9C and 9D are diagrams illustrating the position of the fine-movement stage when the wafer is mounted: FIG. 9C is a diagram as seen from the x-axis direction; and FIG. 9D is a diagram as seen from the y-axis direction.
As can be understood from FIGS. 9C and 9D, when the wafer is mounted, the top plate 11 retracts in the lower z-axis direction. As a result, the upper end of an object temporary mounting member 27 (the object temporary mounting member being a wafer temporary mounting member in this case) fixed to the intermediate plate 12 is above relative to the top plate 11. At that time, the conveying system leaves after mounting the wafer on the object temporary mounting member 27. Then, the top plate 11 moves in the upper z-axis direction, and remounts the wafer from above the object temporary mounting member 27 onto the top plate 11.
The above-described linear motor utilizes the so-called Lorentz force. According to excellent control characteristics of the linear motor, a vibration insulating property that is a feature of the Lorentz force, and the configuration of the six-axes-control fine-movement stage in which a force is directly applied to the fine-movement top plate, serving as an object to be controlled, positioning accuracy is greatly improved as compared with a fine-movement stage in which a position is controlled via air and a mechanism.
However, the linear motor of this type has the problem that heat generation when supplying current is large. When only very precisely controlling the position of the top plate, heat generation causes no problem because the current is substantially zero. However, when supporting the self-weight of the top plate by the linear motor, large heat generation is produced because a large current continuously flows. Accordingly, appropriate self-weight supporting means is conventionally used for supporting the self-weight of the top plate.
More specifically, conventionally, a coil spring 28 is used as self-weight supporting means for the top plate. In order to prevent degradation of the vibration insulating property of the Lorentz-force-six-axes fine-movement stage, it is desirable to design the coil spring so as to have a spring constant as small as possible.
Furthermore, when delivering the wafer onto the object temporarily mounting member 27, the linear motor must generate a force corresponding to “the moving distance of the top plate in that operation X the spring constant”. Heat generation increases in proportion to the square of the spring constant. It is also desirable to design the coil spring so as to have a small spring constant from this fact.
However, the conventional coil-spring-type self-weight support has the following problems.
One is a problem relating to a load when a small spring constant is provided. As the spring constant is selected to be smaller, the amount of deflection of the spring is larger for the same load. If the deflection is large, the top plate reaches the intermediate plate. In order to prevent the top plate from reaching the intermediate plate, the spring constant must be more or less large. As a result, vibration from the base plate is transmitted to the top plate, or heat generation when mounting the wafer is large.
Another problem is vibration of the spring itself when a small spring constant is provided.